This invention relates generally to breathing apparatus and more particularly to controlling the supply of a flow of respiratory treatment gases to a human being as an intermittent gas flow that results in no gas flow during exhalation by the user.
Breathing apparatus in which gas flow is triggered by a human user's spontaneous demand are known. The known apparatus require inhalation to be sensed by a mouth piece or by a tight fitting mask that fits over the mouth and nose to prevent loss of the sensing of inhalation negative pressure. In an attempt to find a more comfortable means to detect inhalation, nasal cannulas have been employed both to sense inhalation and to deliver respiratory gases.
The use of nasal cannula for such dual purposes makes it possible to determine the on-set of inspiration to trigger delivery of a specific dose of a respiratory gas. It is impossible to determine the dose of respiratory gas as a function of the time of inspiration, because it is impossible to both sense and deliver the respiratory gas at the same time when the cannula is used for a dual purpose. The supplying of a large fixed dose of respiratory gas at an early stage of inspiration overlooks the fact that the breathing of a human being is subject to spontaneous changes, and that breathing is a rhythmical act controlled by special control centers in the human brain stem. The rate and depth of breathing are principally controlled by the oxygen and carbon dioxide levels in the arterial blood acting through a classical feedback loop. A fixed dose of respiratory gas cannot provide for the requirements of a human being since the rate of breathing is subject to spontaneous change due to sleeping, exercising, etc. and, therefore, such a method is not satisfactory.
The use of a nasal cannula has a number of other disadvantages when used for both sensing inhalation and delivering of the respiratory gas:
A--The nasal cannula cannot sense inhalation when a human being breaths through his mouth, which often occurs during sleep or when the air passageways in the nose are not open.
B--The nasal cannula cannot be used with humidifiers when it is delivering a respiratory gas, since it is possible for sufficient moisture to accumulate in the supply tubing making it impossible to sense inhalation by the same tube.
If a breathing apparatus is required for such use as oxygen therapy, it is necessary that it function during periods of sleep. Studies reveal that patients receiving oxygen for at least 15 hours per day have almost a 50% better survival rate than those having no supplemental oxygen when such patients have advanced bronchitis or emphysema with defined abnormal airway function and stable partial pressure for oxygen in alveolar gas of less than 60 mm Hg. (Oxygen Therapy - P. Howard).
The present invention overcomes these disadvantages by separating the sensing function from the delivery of the respiratory gas function.
Sensing of inhalation can be accomplished by the Dietz invention by selecting one of two ways, the first is by using a "Pneumatic Breathing Belt Sensor With Minimum Space Maintaining Tapes" (Dietz U.S. Pat. No. 4,602,643 of July 29, 1986). This pneumatic breathing belt sensor detects the expansion and contraction of the chest, abdomen, side or back, by pneumatic means. Expansion of the chest is changed into a positive flow of air (pressure) when inhalation takes place. Contraction of the chest is changed into a negative flow of air (vacuum) when exhalation takes place. The sensor, in the form of a belt with minimum space-maintaining tapes, is worn by the human user and is connected to an appropriate monitor by means of tubing.
The minimum space-maintaining tapes allows the human freedom of movement and prevents such body movements from affecting the operation of the sensor. On inspiration, a dome-shaped diaphragm contracts, the adbominal contents are forced down and forward, and the rib cage is lifted. Both increase the volume of the thorax (or chest).
Respiratory gas is made to flow each time there is a positive pressure flowing from the pneumatic breathing belt, which occurs whenever inhalation is taking place, which results in an increased volume and expansion of the chest.
The second way the present invention can sense inhalation is by means of a two prong nasal cannula. One prong is used for delivery of the respiratory gas and the second prong is used for sensing inhalation.
This method of sensing can be used as an alternate method when the human being is fully aware and capable of determining if breathing through the nose is taking place, and does not wish to wear the pneumatic breathing belt for certain activities.
However, it has the disadvantage that if the wearer falls asleep and breaths through the mouth, the sensor will not function.
The positive flow of air of the pneumatic breathing belt can be detected by using an optoelectronic inhalation sensor (Dietz patent application Ser. No. 06/916,660 Filed 10/06/86, for which a Notice of Allowance has been issued) as a differential pressure switch to measure the flow of air by use of an orifice to obtain differential pressure.
This optoelectronic inhalation sensor contained in the breathing apparatus can also be used to detect the negative pressure of the one prong (used for sensing) of the two prong nasal cannula when inhalation takes place.
The preferred embodiment is to use the optoelectronic inhalation sensor. However, a Microbridge Mass Airflow Sensor, such as the AWM2100V manufactured by the Micro Switch Division of Honeywell can be used to detect the positive air flow of the pneumatic breathing belt or the negative pressure of the one sensing prong of the two prong nasal cannula when inhalation takes place. The advantage of using the optoelectronic inhalation sensor is that the Microbridge Mass Airflow Sensor is more affected by moisture, and requires a filter to be used in line which reduces its sensitivity. It also requires a higher voltage dual power supply, and higher power requirements that results in shorter battery life of portable equipment.
Since the respiratory gas supply is separate from the sensing means, there is no possibility of feedback between the two, and non-detection of apnea by the sensor can not occur due to parasitic oscillations.
The breathing apparatus supply of respiratory gas can be delivered with simple nasal cannula for daytime use and with a loose fitting mouth nose mask for night-time use when the human is sleeping.
Where the breathing apparatus is used in industrial applications, it is possible to supply a controlled high rate of flow of respiratory air for breathing and a lower continuous rate of flow to assure that a hood or mask is always at a positive pressure to flush out contaminants from being breathed in from the outside environment when the pneumatic breathing belt is used.
The prior art (U.S. Pat. No. 3,400,713), in using belts to detect respiration, has considerable delay between the movement of the chest and the operation of the valve controlling the flow of respiratory gas as such devices are completely mechanical and did not use modern electronic methods.
The Dietz invention overcomes this problem due to the extreme sensitivity of the Optoelectronic Inhalation Sensor which is actuated by pressures as low as 0.001 of an ounce per square inch. The valve is operated by an outside source of energy and not dependent on belt pressure to perform the valving function.
The pneumatic breathing belt with minimum space-maintaining tapes, makes the use of a belt practical because it allows freedom of movement and prevents body movements from affecting the operation of the sensor.